This invention relates to the field of integrated circuit fabrication. More particularly, this invention relates to power and ground distribution within a monolithic integrated circuit.
Integrated circuits require both power and ground in order to operate properly. Power and ground are brought in to the integrated circuit through power and ground bonding pads, respectively, which are in turn electrically connected to separate power and ground rings, commonly called core rings. Power and ground are then distributed throughout the integrated circuit via a power mesh and a ground mesh. Individual devices, such as input output circuits, called input cells for simplicity herein, then tap into the power and ground supplies as needed by making electrical connections to the nearest mesh element.
Current core ring design schemes typically place core rings on the two layers below the top-most mesh layer, with the horizontal segments created on one layer and the vertical segments created on the other layer, where the direction of the core ring segments usually matches the preferred routing direction of the corresponding layer.
Current core ring design schemes also typically require that no devices are placed under the core ring and in the area between the core ring and the input cells. This reduces the area available for device placement and tends to increase the die size. Although rectilinear core rings could be used in some cases of different height input cells, any implementation of such core rings tends to be ineffective due to the space requirements for jogging the core ring in order to trace the input cell outline, significantly reducing the benefit of such rings.
With the introduction of multiple height input cells and rectilinear core rings, different numbers of power pads are required depending on the height of the input cells and the distance between the bonding pad and the core ring in order to meet the voltage drop requirements. Such requirements are very complicated to follow, and the required number of pads may be too high for very high inputs, resulting in an increase in the die size, which reduces the effectiveness of pad over input cell designs.
What is needed, therefore, is a power and ground distribution design that requires fewer layers and less surface area to provide power and ground from bonding pads to input cells and other devices, while keeping voltage losses at a low value.
The above and other needs are met by an integrated circuit with a power and ground distribution system having a first electrically conductive layer, a second electrically conductive layer, and an electrically insulating layer disposed between the first electrically conductive layer and the second electrically conductive layer. A first termination ring is formed in the first electrically conductive layer, where the first termination ring forms a first closed loop around a peripheral portion of the integrated circuit. First pad straps are also formed in the first electrically conductive layer, where the first pad straps have electrical connections to the first termination ring. First horizontal mesh members are additionally formed in the first electrically conductive layer, where the first horizontal mesh members have electrical connections to the first termination ring. Second horizontal mesh members are further formed in the first electrically conductive layer, where the second horizontal mesh members do not have electrical connections to the first termination ring.
A second termination ring is formed in the second electrically conductive layer, where the second termination ring forms a second closed loop around the peripheral portion of the integrated circuit. The second termination ring is interleaved with the first termination ring. Second pad straps are also formed in the second electrically conductive layer, where the second pad straps have electrical connections to the second termination ring. Second vertical mesh members are additionally formed in the second electrically conductive layer, where the second vertical mesh members have electrical connections to the second termination ring. First vertical mesh members are further formed in the second electrically conductive layer, where the first vertical mesh members do not have electrical connections to the second termination ring.
First electrically conductive vias in the electrically insulating layer form electrical connections between the first vertical mesh members formed in the second electrically conductive layer and the first termination ring formed in the first electrically conductive layer. Similarly, second electrically conductive vias in the electrically insulating layer form electrical connections between the second horizontal mesh members formed in the first electrically conductive layer and the second termination ring formed in the second electrically conductive layer.
The first termination ring, first pad straps, first horizontal mesh members, first vertical mesh members, and first electrically conductive vias form a first distribution subsystem, and the second termination ring, second pad straps, second horizontal mesh members, second vertical mesh members, and second electrically conductive vias form a second distribution subsystem.
In this manner, the power and ground distribution systems are formed using only two electrically conductive layers, with an intervening electrically insulating layer. With this design, either of the first distribution subsystem or the second distribution subsystem may be assigned as the power or ground distribution subsystem. Further, the vias which interconnect the elements of each subsystem need only pass through one intermediate layer, and thus do not interfere with routing layers. In addition, input cells can be placed directly below the termination rings, thus enabling greater freedom in input cell placement and input cell configuration.
In various preferred embodiments of the invention, the first distribution subsystem is a power distribution subsystem and the second distribution subsystem is a ground distribution subsystem. Alternately, the first distribution subsystem is a ground distribution subsystem and the second distribution subsystem is a power distribution subsystem. Preferably, both the first distribution subsystem and the second distribution subsystem are formed substantially of copper. The first distribution subsystem and the second distribution subsystem preferably overlie the input cells of the integrated circuit.
The first pad straps preferably make electrical connections to first bonding pads, and the second pad straps preferably make electrical connections to second bonding pads. Preferably, portions of the first pad straps are additionally formed in the second electrically conductive layer and make electrical connections to the first pad straps in the first electrically conductive layer through a first series of electrically conductive vias. Similarly, portions of the second pad straps are preferably additionally formed in the first electrically conductive layer and make electrical connections to the second pad straps in the second electrically conductive layer through a second series of electrically conductive vias. In one embodiment the first electrically conductive layer overlies the second electrically conductive layer, and in an alternate embodiment the second electrically conductive layer overlies the first electrically conductive layer.